The present application relates to a system for detecting the presence of an occupant of a seat. More particularly, the application relates to a capacitive sensing system for detecting the presence of a person. In a disclosed embodiment, the system is used for detecting the presence of an occupant in a vehicle seat.
Conductive ink screen printing as well as other methods of delivery have been used to print conductors for use in sensing pads. However, the present application discloses the additional novel approach of creating multiple sensing zones in the sensing pad by printing or screening one or more resistive zones in series with the conductive trace. For example, the present application discloses printing or screening highly conductive material (e.g., silver (Ag)) with varying gaps. A lower conductive carbon based material may be screened over the silver and the gap to create a resistive zone that acts as a resistor in series. The resistive zones' resistance values may be controlled by a number of factors, such as gap length, carbon geometry, etc. A discrete resistor network may be designed using the printing process. The value of each resistive zone could be the same or different depending on system operation and configuration.
For example, the system may be formed using just two different conductivity screen/print inks to create multiple resistive zones of different resistive values to use in forming a network of sensing zones. A highly conductive silver ink and a much less conductive carbon ink may be printed to create a single sheet, multi-zone network that could be used to sense occupant location in a seat. The present application discloses this novel approach to construction of a network of resistive zones (and thereby multiple sensing zones) on a single substrate or base layer.
Existing multi-zone sensors are very complicated with many electric connectors or terminals to account for the multiple zones. For instance, each zone may require one or more electric connector making the systems less reliable and more costly. The present application discloses an improved method of connecting the sensing zones together in an integrated fashion by using resistive material.
By connecting the various sensing zones together via a resistor network, the controller may be configured to determine the zones that are active (i.e., sensing the presence of an occupant) and how much weight is being applied using methods and technology that is similar to that employed in existing capacitive or electric field sensors. With a network of resistive zones acting as resistors in series with the sensing zones, only two electronic connectors are required for potentially any number of zones. The system is only limited by the number of resistors and sensing zones that could be isolated and analyzed by the associated hardware and software.
The disclosed system uses an inexpensive combination of conductive inks to manufacture the system. The use of well-known and understood manufacturing processes fits well with timing, quality and cost for such a system. The reduction of electronic connectors increases reliability of the system significantly and reduces the wire and connector content. All of these benefits lead to a very affordable system with greater capability to detect and distinguish occupant size and position for airbag deployment.
It would be desirable to have a system that uses an inexpensive combination of conductive and resistive inks and a reduced number of electronic connectors in order to produce a more economical occupant detection system.